Acid metal electroplating bath containing an organic sulfonic acid-thioureadithiocarbamic acid reaction product



United States Patent 34 Claims. in. 204-52 This invention relates to a method and bath for obtaining bright, level electrodeposits of metals wherein the bath composition is greatly simplified.

We have found that organic sulfonic acids or their salts, which contain at least one thiourea radical and at least one dithiocarbamic acid radical in the molecule, produce simultaneously excellent brightening and leveling eifects in acid metal electroplating baths, especially in copper electroplating baths.

Such effects could heretofore be achieved only by a combination of diiferent brightening and leveling agents, which often also required further additives, such as porosity prevention, equalizing and wetting agents and/0r agents for increasing the temperature tolerance.

Thus, the employment of the agents according to the invention provides a substantial simplification of the baths with simultaneous improvement of the quality of the metal electroplates. These products possess excellent -full brightening and strong leveling properties, coupled with a temperature tolerance which is suificient tor all practical requirements, so that with the aid of these products the preparation and upkeep Of metal electroplating baths, especially of highsperformance bright copper electroplating baths, becomes substantial-1y simpler. The above-mentioned sulfonic acids can not only be employed in copper electroplating baths, in which they or their salts produce a particularly remarkable effect, but also to good advantage in electroplating baths which contain the salts of the metals zinc, lead, tin and cadmium or mixtures thereof.

It is therefore an object of this invention to provide a method and bath for the electrodeposition of metals wherein the bath composition is greatly simplified.

Another object is to provide a method and bath for electroplating wherein a single additive compound produces bright, level and non-porous electrodeposits of metals.

These and other objects of our invention will become apparent as the description thereof proceeds.

The sulfonic acids or their salts which are employed in accordance with the present invention, may be prepared in simple fashion by well known methods. In general, they are characterized by at least one dithiocarbamic acid group of the general formula in which R and R represent hydrogen or hydrocarbon radicals. Suitable such radicals are identical or different alkyl radicals which may possibly be substituted or, with inclusion of the nitrogen atom, may also together form a heterocyclic ring, such as a monpholine or piperazine ring, or also cycloalkyl radicals.

The sul fonic acids according to the present invention "Ice are also characterized by at least one thiourea group of the general formula in which R and R represent hydrogen, alkyl radicals, cycloalkyl radicals, substituted or unsubstituted aryl radicals or also dithiocarbamic acid radicals attached to the nitrogen through an acyclic or cyclic intermediate mem her, as already described above.

Finally, the sulfonic acids according to the present invention contain an alkyl sul-fonic acid group of the general formula in which R, is a low molecular alkyl radical with 1 to 4 carbon atoms. 7

1 Such compounds may be widely varied, and are indicated by the following general groups represented in the tollowing structural ifonmulas:

wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocyiclic radicals wherein -R may be a tree valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals .wherein R and R may join to fiorm a heterocyclic ring; R is selected from the group consisting of aliphatic, dialkylamino, cycloaliphatic and heterocyclic radicals; Y is a member selected from the group consisting of :8 and X is selected from the group consisting of hydrogen and cation: n is a number at least 1. The R radical is 3 joined to an atom selected from the group consisting of nitrogen and sulfur atoms having free valences. As indicated by the brackets, the R radical may be joined at more than one point in the molecule, such as to the R radical when it represents a free valence, or to the R radical when it is a dialky'larnino radical with a free valence on the nitrogen. R is also being joined to both open sulfur valences in Formula IV It is to be understood that the R radical always carries the sulfonic acid or sulfonate group.

An example of the sulfonic acids or their sodium salts of the type contemplated by the present invention is the di sodi-um salt of l-ipheny lth-i-oureido-3,6-diazahexamethy1- one-3,6-bis-(dithiocarbamic acid propylester w sulfonic acid) of the formula S= S(CHz)a.SOaNa S S(CH .SOaNa which was obtained trom diethylene triamine and phenyl mustard Dill which form N-phenyl-N'-3,6-diaza-hexylthiourea and further reaction of this compound with carbon disulfide and propane sultone in the following manner.

0.5 mol of phenyl mustard oil was added dropwise at 30-35 C. to a solution of 0.5 mol of diethylene triamine in 300 cc. of ethanol, and the mixture was stirred for an additional two hours. Thereafter, 1 mol of sodium hydroxide dissolved in 150 cc. of water was added, and then 1 mol of carbon dis-ulfide was added dropwise to the solution at 40 C. The mixture was then stirred for twenty minutes while increasing the temperature to 60 C., and thereafter 1 mol of molten propane suiltone was added dropwise. After a few hours of boiling under reflux, the mixture was evaporated in vacuo. The sultonic acid salt obtained thereby was triturated with acetone, filtered, washed with acetone and dried in vacuo. 232 gm. (=60% of theory) of the sulfonic acid salt were obtained in the form of a yellowish powder, which was readily soluble in water, exhibited no melting point and decomposed gradually beginning at 200 C. when heated.

A further example of the sulfionic acids according to the present invention is 4-thiohexahydrod,3,5-triazinyll-ethyldithiocarbamic acid propylester-w-sultoni'c acid The sodium salt of this sulfionic acid was obtained by condensation of the sodium salt of aminoethyldithiocarbarnic acid propylesterw-sulfonic acid with thiourea and [formaldehyde with good yields in the for-m of a yellowish powder which had no melting point.

This compound was prepared in the following manner: 13.6 gm. of the inner salt of Z-aminoethyldithio'carbamic acid were dissolved in 100 cc. of water. The resulting solution was admixed with 4 gm. of sodium hydroxide dissolved in 50 ml. of water, 7.6 gm. of thiourea were added and after the latter had dissolved 17.2 gm. of 35% formaldehyde solution were added over a period of evaporated in vacuo. The residue thus obtained was stirred for forty-five minutes and was then allowed to stand overnight, after which the clear green solution was evaporated in vacuo. The resldue thus obtained was taken up in 200 cc. of ethanol, the solution was heated to 70 C. and 12.2 gm. of propane sultone were added dropwise. Thereafter, the mixture was stirred for one hour at 65 C., and after cooling the precipitated substance was separated by vacuum filtration, washed first with ethanol, then with ether and dried in vacuo at 100 C. Yield: 30.7 gm.

This product Was prepared as follows: a solution of 73 gm. of l-(B-aminoethyl)-2-cimidazolinethione, which had been prepared from thiourea and .diethy-lene triamine according to United States Patent No. 2,613,212, in 500 cc. of ethanol was admixed with a solution of 20.2 gm. of sodium hydroxide in cc. of water, 38.3 gm. of carbon di-sulfide were added dl'OPtWElSC in a temperature range of 35-40 C. and then 6 1.5 gm. of molten propane sultone were added slowly over a .period of twenty-five minutes at 6570 C. Thereafiter, the mixture was stirred for two and one-halt hours at 65-70" C. and was allowed to stand overnight. -It was then evaporated in vacuo, the residue was triturated in acetone, vacuum filtered, washed with acetone and dried. 177.8 gm. of a solid product were thus obtained.

91.3 gm. of the product thus obtained were dissolved in a mixture of 225 cc. of water and 375 cc. of ethanol, and 30.5 gm. of molten propane su'ltone were added dropwise to this solution while refluxing it over a period of ten minutes. The mixture was then stirred for an additional hour under reflux, allowed to cool and the cooled solution was filtered. The filtrate was extracted once by shaking with ether, the phase which separated [from the ether was isolated and acetone was added thereto, whereby a solid substance precipitated out which was dried in vacuo after decanting the liquid and washing the solid once with acetone. 66 gm. of a faintly yellow, water-soluble substance were obtained.

Analysis (C H gN NaO -S Molecular weight=487. Calculated: C, 29.60%; H, 4.52%. Found: C, 30.25%; H, 4.61%.

Other sulfonic acids or their salts which may be employed in accordance with the present invention are those in which the dithiocarbamic acid group is connected with that portion of the molecule which contains the thiourea and the sulfonic acid radical through an ester bond. An example of such a substance is the reaction product of N,N' bis (diethylthiocarbamyl-mercaptomethyl)-thiourea with propane sultone, which has the following formula:

The linkage between the dithiocarbamic acid radical and the thiourea radical, which in the case of the above compound (No. 4) is formed by a methylene group, may also be formed by other groups, such as by an ethylene or propylene group or by another hydrocarbon radical, which may also be substituted or interrupted by hetero atoms or may be closed into a heterocyclic ring including the two nitrogen atoms, such as a piperazine ring.

The alkyl sulfonic acid radicals are attached to the.

molecule through sulfur or nitrogen and preferably attached to the dithiocarbamic acid and/or thiourea moieties. It is upon this combination of these radicals that the special full brightening and leveling effect of the products according to the present invention is based.

Further illustrations of suitable sulfonic acids also include the following compounds which comprise the gm. per liter of N,N,N',N-tetraethyl-1,3-diaminopropanel-2. A bath having this composition produces uniformly full bright and satisfactory level copper electroplates in a current density range of 0.3 to 8 amp/dm. and at a temperature tolerance of 10 to 38 C. The copper electroplates are ductile and free from pores. They completely level a 280-grain etched area with a thickness of 20,11. without further additives.

Example 11 0.1 gm. per liter of compound No. 8 are added to an acid copper plating bath which contains 210 gm. per liter of copper sulfate, CuSO -5H O, 60 gm. per liter of sulfuric acid, 1 gm. per liter of the addition product of mols of ethylene oxide to 1 mol of a coconut fatty alcohol mixture and 0.02 gm. per liter of thioflavin. A bath of this composition produces ductile, pore-free, uniformly full bright and satisfactorily leveling copper electroplates in a current density range of 0.2 to 8 amp/dm. at a temperature tolerance of 10 to 38 C. A 280-grain etched GE -CH3 II S 2 2 Example 111 S ll It has further been found that sulfonic acids which contain aromatic radicals in the molecule, such as phenyl, tolyl, xylyl, naphthyl, diphenyl radicals, etc., exhibit particularly favorable brightening, strongly leveling, good equalizing and, in many cases, also wetting properties in addition to a temperature tolerance which is adequate for all practical requirements, so that they make it possible to prepare a single component bath or, in the event that their properties as wetting agents are not sufiiciently distinct, the preparation of at least a two-component bath.

The agents according to the present invention are added to the electroplating bath in amounts of 50 mg. to 5 gm. per liter, preferably in amounts of 100 to 500 mg. per liter of bath fluid. The employment of the additives does not require special measures; they are readily soluble in the acid metal salt baths in the required quantity and also .exhibit satisfactory stability during the operation of the electroplating bath. If necessary, they may also be employed in combination with other known electroplating chemicals.

The following specific examples are presented to illustrate the invention and to enable persons skilled in the art to better understand and practice the invention and are not intended to be limitative.

Example I 0.2 gm. per liter of compound No. 4 are added to an acid copper plating bath which contains 210 gm. per liter of copper sulfate, CuSO -5H O, 80 gm. per liter of sulfuric acid, 2 gm. per liter of the addition product of 18 mols of ethylene oxide to 1 mol of nonylphenol and 0.25

When the acid electroplating bath described in Example II is modified with 0.11 gm. per liter of compound No. 7 as the brightening and leveling agent, the same good results as described in Example H are obtained.

Example IV 0.20 gm. per liter of compound No. 2 are added to an acid copper plating bath which contains 220 gm. per liter of copper sulfate, CuSO -5H O, 60 gm. per liter of sulfuric acid and 1 gm. per liter of the addition product of 18 mols of ethylene oxide to 1 mol of nonylphenol. The addition of a further'component is not'necessary. The copper electroplates obtained thereby are ductile, free from pores, have a uniform full brightness and a good leveling efliect in the current density range of 0.2 to 8 amp/din. and at a temperature tolerance of 10 to 38 C. A 250-grain etching is completely leveled by a cop, per deposit 201:. thick.

If the above-described bath is operated without the addition of a wetting agent, equally good results are obtained with respect to the quality of the copper deposits, but preferably in a somewhat narrower current density range of -1.5 to 8 amp/dm.

Example V 0.10 gm. per liter of compound No. 3 are added to an acid copper plating bath which contains 210 gm. per liter of copper sulfate, CuSO -5H O, 60 gm. per liter of sulfuric acid and 1 gm. per liter of the addition product of 20 mols of ethylene oxide to 1 mol of a coconut fatty alcohol mixture. The addition of a further component is not necessary. Ductile, pore-free, uniformly full bright and satisfactorily leveling copper deposits are obtained in a current density range of 0.5 to 10 amp/dm. and rat a temperature tolerance of 10 to 38 C. A 280-grain etched area is completely leveled by a copper deposit of 20p thickness.

Example V1 0.5 gm. per liter of compound No. 1 are added to an acid copper electroplating bath which contains 210 gm. per liter of copper sulfate, CuSO -5H O, and 60 gm. per liter of sulfuric acid. The addition of further assistants is not necessary because the bath having this simple composition already furnishes ductile, pore-free, uniformly tull bright and satisfactorily leveling copper electroplates (in a current density range of 0.5 to 8 amp/dm. at a temperature tolerance of 1-0 to 35 C. A ZZO-grain etched area is completely leveled by a copper deposit having a thickness of 20p. -A further advantage of this 'bath resides in that it can be operated without difiiculties with air.

Example VII 0.4 gm. per liter of the compound No. 5 are added to an acid copper electroplating bath which contains 210 gm. per liter of copper sulfate, CuSO *5H O, and 60 gm. per liter of sulfuric acid. The addition of a further component is also unnecessary in this case. Ductile, pore-free, uniformly full bright and satisfactorily leveling copper electroplates are obtained in a current density range of 0.5 to 8 amp/dm. and at a temperature tolerance of 10 to 35 C. A 220-grain etched area is completely leveled by a copper deposit having a thickness of This bath can also be operated with air in an advantageous manner.

Example VIII 0.15 gm. per liter of compound No. 5 is added to an acid zinc electroplating bath which contains 300 gm. per liter of zinc sulfate, 10 gm. per liter of aluminum sulfate wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocyclic radicals wherein R may be a free valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R and R may join to form a heterocyclic ring; R is selected from the group consisting of aliphatic, dia'lkylamino, cycloaliphatic and lheterocyclic radicals; Y is a member selected from the group consisting of Q and X is selected from the group consisting of hydrogen and cations; and n is a number at least 1; said R radical being "joined to an atom selected from the group consisting of .and 20 gm. per liter of boric acid. The bath is operated in a pH range between 3 and 5 and furnishes bright, ductile, very fine-grained zinc electrodeposits which adhere well to the iron surface in a current density range of 0.5 to 8 amp/dm. at a temperature tolerance of 15 to 30 C.

While We have set forth certain specific examples and preferred modes of practice of our invention, it Will be understood that this is solely for the purpose of illustration and that various changes and modifications may be made without departing from the spirit of the disclosure and the scope of the appended claims.

We claim:

1. A process for producing bright, smooth deposits of metals capable of being electrodeposited selected from the group consisting of copper, zinc, lead, tin and cadmium which comprises depositing the metal from a bath containing the metal to be deposited in the form of an aqueous solution of an inorganic salt thereof in the presence of an additive compound having a structural formula selected from the group consisting of:

S= S(CHz)a-SOzNa S 3. The process of claim 1 wherein the additive compound is:

5. The process of claim 1 wherein the additive compound is:

7. The process of claim 1 wherein the additive compound is:

i 8. The process of claim 1 wherein the additive compound is:

s (lHzhSOr 9. The process of claim 1 wherein the additive compound is:

HIN(|.?NHCH2*S(fi-NHC Hz-C HzC H3-S O 3N8,

10. The process of claim 1 wherein the additive compound is:

from the group consisting of aliphatic, dialkylamino, cy-

11. The process of claim 1 wherein the additive compound is:

12. The process of claim 1 wherein the additive compound is:

S QaNa 13. The process of claim 1 wherein the additive compound is:

14. The process of claim 1 wherein the additive compound is:

cloalipha-tic and heterocyclic radicals; Y is a member selected from the group consisting of S and X is selected from the group consisting of hydrogen and cations; and n is a number at least :1; said R radical being joined to an atom selected from the group consisting of nitrogen and sulfur atoms having free valences; said additive compound being present in sufficient amount to eifect said brightening and smoothing.

16. A process for producing bright, smooth deposits of metals capable of being electrodeposited selected from the group consisting of copper, zinc, lead, tin and cadmium which comprises depositing the metal from a bath containing the metal to be deposited in the form of an aqueous solution of an inorganic saltthereof in the presence of about 100 to 500 rug/l. of bath of an additive compound having a structural formula selected from th group consisting of:

wherein R and R are selected from the group consisting 'lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R and R may join to form a heterocyclic ring; R is selected from the group consisting of aliphatic, dialkylamino, cycloaliphatic and heterocyclic radicals; Y is a member selected from the group consisting of :S and SR 4O X X is selected from the group consisting of hydrogen and cations; and n is a number at least 1; said R radical being joined to an atom selected from the group consisting of nitrogen and sulfur atoms having free valences; said additive compound being present in sufficient amount to effect said brightening and smoothing.

17. A process for producing bright, smooth deposits of copper which comprises depositing said copper from a bath containing an aqueous solution of an inorganic salt of copper in the presence of an additive compound having a structural formula selected from the group conll 2 nitrogen and sulfur atoms having free valences; said additive compound being present in suflicient amount to efiect said brightening and smoothing.

18. An electroplating bath for producing bright,

"smooth electrodeposits of metals capable of being electr0- deposited selected from the group consisting of copper, zinc, lead, tin and cadmium comprising an aqueous solution of an inorganic salt of the metal to be deposited and 'an additive compound having a structural formula selected from the group consisting of:

wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocyclic radicals wherein R may be a free valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R and R may join to form a heterocyclic ring; R is selected from the group consisting of aliphatic, dialkylamino, cycloaliphatic and heterocyclic radicals; Y is a member selected from .the group consisting of 8 and --SR SO X,,; X is selected from the group consisting of hydrogen and cations; and n is a number at least 1; said R radical being joined to an atom selected from the group consisting of nitrogen and sulfur atoms having free valences; said additive comp'ound being present in sufficient amount to effect said brightening and smoothing.

19. The bath of claim 18 wherein the additive compound is:

QNH-(if-NH-ClI -C HrN-CHr-CHr-NH-O-S-(CHI) 3.8 OaNa wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocyclic radicals wherein R may be a free valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R and R may join to form a heterocyclic ring; R is selected from the group consisting of aliphatic, dialkylamino, cycloaliphatic and heterocyclic radicals; Y is a member selected from the group consisting of :8 and -S--R SO X X is selected from the group consisting of hydrogen and cations; and n is a number at least 1; said R radical being joined to an atom selected from the group consisting of 13 22. The bath of claim 18 wherein the additive compound is:

N-o s-onrNn-c=1iH-0Hhsc-N CQ g S -(CHflaSOa' S \C2H5 2s. The bath of claim 18 wherein the additive compound is:

S(CH:)3SO3' S C2H5 24. The bath of claim '18 wherein the additive com- 27. The bath of claim 18 wherein the additivecompound is: r 1 v wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocyclic radicals wherein R may be a free valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R aud R may join to form a heterocyclic ring; R is selected from the group consisting of aliphatic, dialkylamino, cycloaliphatic and heterocyclic radicals;

28. The bath of claim 18 wherein the additive compound is: p 7 p I (JET-CH3 flQas DPN 1 e ch, S. S I /HmSOr 29. The bath of claim 18' wherein the pound is:

additive com- I Y is a member selected from the group consisting of Q and SR SO X X is selected from the group CH OH2 j I onr-on,

consisting of hydrogen and cations; and n is a number at least 1, said Rt radical being joined to an atom se- SOaNa 30. The bath of claim 18 wherein the additive compound is:

31. The bath of claim 18 wherein the additive compound is:

32. An electroplating bath for producing bright, smooth electrodeposits of metals capable of being electrodeposited selected from the group consisting of copper, zinc, lead, tin and cadmium comprising an aqueous solution of an inorganic salt of the metal to be deposited and about mg. to 5 g./l. of bath of an additive compound having a structural formula selected from the group consisting of:

lected from the group consisting of nitrogen and sulfur atoms having free valences.

33. An electroplating bath for producing bright, smooth electrodeposits of metals capable of being electrodeposited selected from the group consisting of copper, zinc, lead, tin and cadmium comprising an aqueous solution of an inorganic salt of the metal to be deposited and about to 500 mg./1. of bath of an additive compound having a structural formula selected from the group consisting of:

wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocylic radicals wherein R may be a free valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R; is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R and R may join to form a heterocyclic ring; R, is selected from the group consisting of aliphatitic, dialkylamino, cycloaliphatic and heterocyclic radicals; Y is a member selected from the group consisting of :8 and S-,R SO X,,; X is selected from the group consisting of hydrogen and cations; and n is a number at least 1; said R -radical being joined to an atom selected from the group consisting of nitrogen and sulfur atoms having free valences.

v 34. An electroplating bath for producing bright, smooth electrodeposits of copper comprising an aqueous solution of an inorganic salt of copper and an additive compound having a structural formula selected from .the group consisting of:

wherein R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and taken together, heterocyclic radicals wherein R may be a free valence; R and R are selected from the group consisting of hydrogen, aliphatic, cycloaliphatic and aryl radicals; R is a lower alkyl radical; R is selected from the group consisting of hydrogen and aliphatic radicals wherein R and R may join to form a heterocyclic ring; R is selected from the group consisting of aliphatic, dialkylamino, cycloaliphatic and heteroeyclic radicals; Y is a member selected from .the group consisting of :S and -S--'R ---S0 X X is selected from the group consisting of hydrogen and cat-ions; and n is a number at least 1, said R radical being joined to an atom selected from the group consisting of nitrogen and sulfur atoms having free valences; said additive compound being present in sufficient amount to elfect said brightening and smoothing.

References Cited by the Examiner UNITED STATES PATENTS 2,837,472 6/58 Gundel et a1 20452 2,910,413 10/59 Strauss et a1. 20452 2,948,752 8/60 Podesva et a1. 260-552 3,006,954 10/61 Ramey et a1. 260-552 JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,203,878 August 31, 1965 Wolf-Dieter Willmund et al.

corrected below.

Column 3, line 65, strike out "evaporated in vacuo. The

residue thus obtained was" and insert instead ten minutes at 20-25 C. The resulting mixture was column 4, line 64, after "another" insert short column 13, claim 24, the

formula should appear as shown below instead of as in the patent:

2 =NH-CH2' column 15, line 24, for "aliphatitic" read aliphatic Signed and sealed this 10th day of May 1966.

(SEAL) Attest:

ERNEST W. .SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

18. AN ELECTROPLATING BATH FOR PRODUCING BRIGHT, SMOOTH ELECTRODEPOSITS OF METALS CAPABLE OF BEING ELECTRODEPOSITED SELECTED FROM THE GROUP CONSISTING OF COPPER, ZINC, LEAD, TIN AND CADMIUM COMPRISING AN AQUEOUS SOLUTION OF AN INORGANIC SALT OF THE METAL TO BE DEPOSITED AND AN ADDITIVE COMPOUND HAVING A STRUCTURAL FORMULA SELECTED FROM THE GROUP CONSISTING OF: 